This section provides background information related to the present disclosure which is not necessarily prior art. This section also provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
Modifying semiconductor surface topography is a common method for enhancing light absorption within various optoelectronic applications. Many surface patterning techniques do not retain the semiconductor's original crystal structure, which leads to efficiency losses within devices. The reason for this is that either ablation or at least melting occurs in all of these techniques, which leads to significant disruption of the lattice. Hence, there is need for surface processing methods that can largely retain a single crystal structure within the patterned region.
The interaction between multiple intense ultrashort laser pulses and solids universally produces a regular surface corrugation. We have identified a coupled mechanism that operates in a specific range of fluences in semiconductors between the band-gap collapse and ultrafast-melt thresholds that produce a unique corrugation known as high spatial frequency laser induced periodic surface structures (HSFL). The structures have period <0.3 times the laser wavelength and are predominately epitaxial single crystal. What makes this process unique is that the corrugation is produced without any melting or ablation. HSFL formation is initiated when the intense laser field softens the interatomic binding potential, which leads to an ultrafast generation of point defects. The interplay between surface plasmon polaritons that localize defect generation and transient surface morphologies driven by strain relaxation, via diffusing defects, results in the evolution and eventual completion of HSFL formation. This process can occur in ambient condition (in air) without the need for a high vacuum system. This is a remarkable finding in itself because it has been commonly believed that epitaxial redistribution near a surface requires a vacuum.
Accordingly, the teachings of the present invention are applicable to a wide range of devices including but not limited to solar cells, batteries, chemical, biological, light sensors, and the like. The ability to process in air makes this novel approach even more attractive for producing a product. Furthermore, this process is easily combined with traditional manufacturing methods for these kinds of devices such as, but not limited to, molecular beam expitaxy, chemical beam expitaxy, gas entrainment deposition, atomic layer deposition, and sputter deposition. Such combinations, along with thermal annealing techniques, greatly enhance our claims as we can produce pn junctions, Schottky or Ohmic contacts, modulation doped layers, etc. to create novel devices.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
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